Kyoto University
The primary objective of sediment control operations is prevent and decrease from sedimentation disasters, and the development of techniques contributing to this objective is necessary. On the other hand, it is also essential matter to maintain fundamental conditions of fluvial ecosystem, consisting of water, sediment and aquatic lives. Therefore, it is necessary for us to make efforts in finding a way to control the sediment in sediment transport systems so as to satisfy both of these two extreme objectives.
In the laboratory, the Sediment Control Engineering is developing methods predicting and decreasing damages from sedimentation disasters and methods evaluating impacts of sediment transport on ecosystem, from two main standpoints of “disaster prevention” and “environment”.
Research topics:
Sediment management in mountain-river-coast systems
As controls of sediment in mountain-river-coast systems, anti-sediment treatments on production areas, sabo dams, and a system of sediment flushing from reservoirs are major tools. Functions of these tools are being investigated not only from a viewpoint of sediment hydraulics but also from a viewpoint of fluvial environments.
As an example of these studies, an evaluation method for impacts of sediment flushing from reservoirs on fishes is being developed. By modeling the processes of changing habitat due to sediment deposition, anoxia and die due to turbidity after sediment flushing, the evaluating method is constructed. Figure 1 shows a relationship between concentration of turbidity, exposed duration and survival ratio of fishes.
As the other topics, evaluation method of sabo dam functions, development of new type sabo dams, study on habitat environment of fishes from a viewpoint of sediment transport, and development of a model analyzing riverbed change as a control of sediment are now focused.
Monitoring sediment routine in mountainous watershed
Understanding sediment routine in mountainous watershed is important for the sediment management in mountain-river-coast systems. However, it is difficult to evaluate timing, location, and amount of sediment production and runoff along headwaters.
We are now developing a new method estimating the timing and amount of sediment productions by means of monitored turbidity which is closely related to the sediment production and runoff, and tracing sediment transport through numerical model calculations.
This study topic is being carried out based on field observations in Hodaka Sedimentation Observatory located on Okuhida Spa Resort, Gifu. Figure 2 shows an example of a relationship between flow rate, turbidity, and precipitation measured in a watershed. By these continuous measurements, it will be possible to record the sediment transport phenomena.
Understanding and predicting sediment production in mountainous areas
In mountainous areas, sediments are generally produced by freeze-thaw effect or slope failures during rainstorm. The production of sediment is not only a starting point of sediment dynamics in sediment transport systems but also a cause of serious disasters. In this sense, it is necessary to understand the process of sediment production and to develop a method predicting its amount and timing.
As an example, we are developing a new method to predict amount of the sediment produced though the freeze-thaw effect, which is one of the dominant causes of sediment production, by means of monitored air temperature, soil temperature, soil water content, and measured soil properties.
Recently, it is pointed out that preferential water flow through soil pipes in hillslope soils might influence occurrence of slope failures. We are now investigating morphological structure, hydrological effects on rainwater flow within the soil profile, influence on slope stability and occurrence of debris flow by clogging and opining, of soil pipes.
Links:
Sediment Control Engineering: https://www.kyoto-u.ac.jp/en/
Laboratory Website: http://rcfcd.dpri.kyoto-u.ac.jp/sabo/index.html